The present invention relates to a method of expanding a regular three-stage switching array wherein the size of switching blocks in the first and third stages is expanded in such a manner that at least two switching blocks are combined in each of the first and third stages to form one larger switching block, and wherein additional switching blocks are added to each of the three stages.
With an increased demand for connections to be switched through, switching arrays must be expanded. A three-stage switching array that can be expanded to an unlimited extent is known from Federal Republic of Germany Patent No. 2,803,065. In this case, switching matrices (hereinafter referred to as switching blocks) in all three stages are expanded. The expansion requires considerable preliminary work, i.e. at a stage in which the extent of expansion cannot even be foreseen, switching blocks must be provided with blind connections. In addition, the switching array is not non-blocking. The same applies for expansion of the switching array according to Federal Republic of Germany Patent No. 1,130,482, which involves only a two-stage array. Federal Republic of Germany Offenlegungsschrift DE-OS 2,424,727 discloses a switching array which is expanded at considerable additional expense via parallel switching blocks.
Moreover, it has been proposed in the inventor's Federal Republic of Germany patent application P 39 06 545.6, filed Mar. 2nd, 1989, the disclosure of which is incorporated herein by reference, to gradually replace the switching blocks in the first and third stages or in the second stage by larger switching blocks. During each replacement of a switching block, the block is disconnected in steps via a redundant block.